Typical containers used in a microwave oven are made of materials that electromagnetic waves can pass, and the materials may be, for example, glass, ceramic, resin, etc.
Materials such as metal that blocks the passing of electromagnetic waves cannot be used in a microwave oven.
However, containers made of metal are very effective for cooking food, not just for simply defrosting food.
A cooking bowl made of resin, not metal, is disclosed in Korean Patent Laid-Open No. 10-2005-0115981. This application relates to a cooking bowl for the microwave oven range, and teaches a cooking bowl with an electric wave absorber, which is formed on a lower part, in a bowl made of resin having heat resistance.
Further, as examples for cooking food in a container made of metal, US Patent Publication No. US2004/0094544 teaches a cooking vessel for heating water by the heat of the lower part of a container, which is located on the lower surface and made of a microwave permeable material, in a structure where a metal lid blocks microwaves, and US Patent Publication No. US2004/0118838 was filed and published in the name of the applicant of the present application, and teaches a vessel for cooking food by using a heating element that is made of ferrite rubber on the lower surface of the vessel made of a heat conductive material.
Meanwhile, such metal bowls have been used to cook food, but a metal travel mug has not been used yet for microwave oven because the material is made of metal such as stainless steel, and when food within the mug gets cold, the mug cannot be used to warm the food up using microwave oven.
Since the size of a mug for microwave oven is very small compared to typical cooking containers, a structure that can be used for microwave oven cannot be made with conventional techniques for cooking containers.